After 8 hours or trying every workaround i could find still no luck. I can only get solo player to work if i change the port in settings to anything other than 30000. trying to load a game i get the error: Server error: Cannot use IP port. Please start only one server instance of the game. I have made sure that the program is set up in both windows firewall and my antivirus, and the router has also been checked and is set up correctly. We know this game works fine on another PC on the network so cant be the router. I have also checked and no other program is using the 30000 port. have tried with antivirus disabled and have tried taking the data files from the PC everything works on and the same issue so we know its not a 'game bug' just trying to set up co op on this PC and its driving us crazy. Have also tried to install and run the dedicated server app from steam however can not get that to open, it opens for a second and closes itself down (not sure if related) confirmed its on allowed for the firewalls. Any help would be good. Thanks.